In a turbo machine such as a steam turbine, a gas turbine, or a turbo compressor, possible leak of an operation fluid such as steam from a gap between a stationary side and a rotating side causes a loss (leak loss) of the efficiency in the turbo machine. With the foregoing problem in view, a turbo machine uses a non-contact seal structure such as a labyrinth seal to avoid leak of an operation fluid.
A known labyrinth seal is of a step type, which includes: a seal member such as a seal fin being arranged in an inner circumference of a casing, which serves as an outer shell of the turbo machine, and extending toward a rotating vane; and a step-form shroud formed on the tip of the rotating vane (e.g., Patent Literature 1).
In such a step-type labyrinth seal, a radius-direction wall along the radius direction of the step section (step seal) of the shroud forms a main vortex of the operation fluid, and the action of a corner of the step section generates a separated vortex (vortex of the separated flow) from the main vortex at the upstream side of the seal fin. This separation vortex provides so-called contraction effect, so that the amount of leak of the operation fluid from the clearance between the seal fin and the shroud can be reduced.